Could someone please tell me if traders, say in the London futures 'daytime trading' market, which opens at 3 AM Eastern Time have to post the full initial margin amount ($4375 USD) for each contract because it is after-hours with respect to the US futures market (9:30 AM to 4:15 PM)? In other words, is it only during US RFTH that reduced margin requirements (like $400/ES contract) can be in effect?

US RFTH (regular futures trading hours) are from 9:30 AM till 4:15 PM ET. As we all know, during that time one can daytrade futures and pay as little as $400/contract. Are you saying that as far as you know, anytime outside that time frame, all over the world, the full margin price per ES contract (currently $4375 USD) must be paid?

US RFTH (regular futures trading hours) are from 9:30 AM till 4:15 PM ET. As we all know, during that time one can daytrade futures and pay as little as $400/contract. Are you saying that as far as you know, anytime outside that time frame, all over the world, the full margin price per ES contract (currently $4375 USD) must be paid?

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Not exactly.You must pay the full margin only to get over settlement hour which is at 3:45 pm est and to hold over days weeks etc.You can use intraday margin which is 400-500$ at ETH Globex starting from 4:15 pm est till 3:45 pm est next day- almost 24 hrs.

So then when one looks at the overseas/overnights and observes not infrequently, a volume increase at 3 AM ET, it may well be someone buying ES contracts at something less than $4375 USD/contract. Correct?

If we move Stateside, then if one is flat at the end of RFTH for Day 1, then, if your broker permits it, one can buy a contract for Day 2 (after 4:15 PM ET) at something less than $4375 USD/contract. Correct?